It is know to use three controllable fluid circuits (three-pass) to provide pressurized fluid to and to drain fluid from the torus and two pressure chambers to control operation of a multi-function torque converter with impeller and torque converter clutches. A pump in a transmission is typically used to provide pressurized fluid for the torque converter and to drain fluid from the torque converter. However, most known transmissions can only provide two controllable fluid circuits making the three-pass design unusable with these transmissions.
For a multi-function torque converter with only two controllable fluid circuits (two-pass), it is known to close the impeller clutch and then to close the torque converter clutch in series. For example, to use the same fluid circuit to provide apply pressure to close both the impeller clutch and the torque converter clutch. However, this process reduces the pressure bandwidth for both clutches. Further, the torque converter clutch-apply pressure for known multi-function torque converters typically starts at a higher level than in a conventional torque converter. As a result, there is need for higher pressure in the circuit and increased pump capacity, and efficiency of the hydraulic system decreases. In addition, with typical multi-function torque converter designs having a two-pass design, it is difficult to control the closing of the impeller clutch; for example, the impeller clutch typically closes too abruptly causing an uncomfortable sensation for the driver of the vehicle including the torque converter.